It isn't enforced as far as i know, it's just what everyone does as it's a very convenient format for a few reasons, namely it's an easy way to catalog their replaymaking route through the times, and it's an easy way for replay viewers to check out what their favourite replay makers have been up to. We usually get rid of threads which have as their sole purpose collecting replays by members of a clan for a clan video or for some reason other than to share them with other people or get comments since they can use their clan board/thread for that, but we don't really demand that every thread be a personal thread (afaik, I haven't been incredibly active so if there was such a case please correct me )
Of course I understand that a lot of people may not know that public threads are allowed since they are a rare sight, so making a few sticky ones sounds like a nice idea.

For reference here is marcus's (once hugely popular) replay thread dedicated to decapitation replays which worked a bit like what you're suggesting. Maybe this could give a vague idea of how a thread like that would go.
We also had a public thread by jisse. It didn't live very long because there was no rule demanding that you comment on other people's replays (in fact there is a rule against it. and also the replays fit for the thread are just not common to come by, people just dumped the weird replays they had made previously and left, myself included.)


Mandatory cnc would be absolutely necessary, otherwise the thread would die off quickly.
I have always liked the idea of public replay threads with obligatory cnc before posting your own replay, that way regardless of how well known you or your thread are you will get some commentary. I'm up for some stickied threads.

I don't know if time limits are necessary, if someone wants to post 5 aikido replays in a day they will have to comment on a 5 replays by other people. Assuming that they aren't bad 3 word comments and they aren't breaking any rules, that doesn't sound like a big problem.